well we were just out there last week.
but you need at least your CAMS level 2S licence, fire extinguisher (mounted correctly), blue triangle on the bonnet to show where the battery is located. you also need to be a member of a car club. have a helmet (obviously) need to wear long sleves (preferably cotton) you need to make sure your bonnet has a secondary latch (if its got a standard bonnet it SHOULD pass)
also it pays to go over your car before you get there to make sure it will pass scruteneering, ie. battery is secured, tyres are good etc...
thats about it, im sure if i have missed anything i will be corrected...